Petroleum refiners are continually seeking to improve refinery throughput and increase the yields of the highest value products, primarily distillate transportation fuels. This is typically accomplished by atmospheric distillation of the lighter components of petroleum crude to produce straight-run naphtha, jet, and diesel fuels that can be readily hydrotreated to remove sulfur, or undergo further catalytic processing to meet gasoline, jet, and diesel fuel specifications. However, typical petroleum crude oils may contain only 40 to 70% straight-run distillate hydrocarbons that boil below 650° F. The goal then is to upgrade the remaining 30 to 60% of atmospheric tower bottoms (ATB) into distillate fuels that boil below 650° F. Petroleum ATB contains metals, asphaltenes, and resins that must be removed before it is converted into lower-boiling compounds via catalytic hydrocracking or fluid catalytic cracking (FCC).
Vacuum distillation of ATB is typically employed to produce vacuum gas oil (VGO) distillate and vacuum tower bottoms (VTB) or residuum that contains most of the contaminants and exhibits an atmospheric equivalent distillation temperature greater than about 1000-1050° F. Vacuum distillation is performed in a manner that VGO produced is sufficiently reduced in asphaltenes, Conradson Carbon Residue (CCR), and metals to permit upgrading into transportation fuels via catalytic hydrocracking or FCC. However, only about 80% of refineries have vacuum distillation systems because they are expensive to build and operate.
The residuum or VTB produced by many refiners still contains valuable hydrocarbons that could be cracked into additional distillate fuels if asphaltene, CCR, and metal content were reduced to acceptable levels. Solvent deasphalting is a refinery process for extracting asphaltenes and resins from ATB, VTB, or other heavy petroleum fractions to produce deasphalted oil (DAO) that is typically hydrotreated before being fed to FCC or hydrocracking systems. One such commercial process is called Residuum Oil Supercritical Extraction or the ROSE process practiced by KBR, Inc. The process consists of contacting the feedstock with volatile solvents, such as propane, butane, or mixtures thereof, in a counter-current extractor at the temperature and pressure needed to precipitate the asphaltene and resin components that are not soluble in the solvent. The solvent deasphalting process requires a considerable amount of solvent, and solvent recovery is an energy-intensive process. The yield of DAO is typically only 40-60%. Higher yields can only be obtained by sacrificing DAO quality. Due to the paraffinic nature of the solvent, paraffins are selectively extracted and recovered in the DAO fraction.
The refining industry would benefit greatly from a process, such as the present invention, that will produce high yields (over 90%) of a clean VGO equivalent from intermediate refinery streams or crude petroleum oil. The clean VGO equivalent is a suitable feed stream for hydrocracking or fluid catalytic cracking due to reduced levels of asphaltene, CCR, and metals content.